{
  "bibcode": "2018GCN.22579....1K",
  "body": "N. P. M. Kuin (UCL-MSSL) and A. Y. Lien (GSFC/UMBC)\nreport on behalf of the Swift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of GRB\n180331B 668 s after the BAT trigger (Lien et al., GCN Circ. 22573).\nNo optical afterglow consistent with the XRT position Goad er al.,\n(GCN Circ. 22575) is detected in the initial UVOT exposures,\nconsistent with the report of Volnova et al.  (GCN Circ. 22577).\nPreliminary 3-sigma upper limits using the UVOT photometric system\n(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first\nfinding chart (FC) exposure and subsequent exposures are:\n\nFilter         T_start(s)   T_stop(s)      Exp(s)         Mag\n\nwhite_FC           668          818          147         >21.2\nwhite              668         2066          412         >21.8\nv                 1056         2115          136         >19.2\nb                 1156         2041          117         >20.3\nu                 1130         2016          117         >20.3\nw1                 849         1992           78         >20.2\n\nThe magnitudes in the table are not corrected for the Galactic extinction\ndue to the reddening of E(B-V) = 0.01 in the direction of the burst\n(Schlegel et al. 1998).",
  "circularId": 22579,
  "createdOn": 1522575535000,
  "email": "npkuin@gmail.com",
  "subject": "GRB 180331B: Swift/UVOT Upper Limits",
  "submitter": "Paul Kuin at MSSL  <npkuin@gmail.com>",
  "eventId": "GRB 180331B"
}